This is based on the assumption that total fees per block will remain static, which as I mentioned above, I don't think they necessarily will.
Most probably the fees will rise as they will not remain static as we are 601 days left from the next halving at block 840,000 when the rewards will be halfed to 3.125
BTC per block and coins in circulation will also reduce but the transaction would increase I would say even if we take into consideration the layer 2 like LN channels and you would pay more to confirm your transactions even if we say in the short span also so the miners profitability is still there.
We already know that block space is too limited as it stands to scale bitcoin to global usage, which is why second layer solutions are being developed.
Yeah in the meantime we may see some more development to tackle the fees issues in much more efficient manner but we are seeing the LN capacity being increased each time and they are being used by many to make regular transactions saving them from fees and LN nodes support being rise with bitcoin block space limitations.
In this scenario then fees per block could total 1-2 BTC, rather than 0.1-0.2 BTC (example numbers), meaning a price of $80k rather than $800k in your example.
If that's the case then it's pretty much efficient for miners to have that much amount in fees only as an extra reward along with bitcoin earned so we can say that they will have around $250k as block reward plus $100k-$160k in fees as well so securing the network would still be profitable fort them and we will see more support from the users as well.